Early in 1952, many processes for the selective hydrogenation of carbon-carbon double bond (C.dbd.C) in NBR were patented. By 1985, numerous patents such as U.S. Pat. Nos. 3,700,637; 3,898,208; 3,480,659; 4,464,515; 4,581,417; 4,503,196; GB 1,558,491; 2,070,023A mainly focused on organo-rhodium complexes, i.e. the so-called Wilkinsons catalysts, of which RhCl(PPh.sub.3).sub.3 was the typical one. The characteristic of Rh-complexes as hydrogenation catalysts in high activity and high selectivity, while their drawback is high cost. Despite of its very small abundance ratio, rhodium is widely used in chemical industry; glass, ceramics and electrical applicance industries; and is an essential component in catalysts for the purification of exhaust gas from automobiles, which renders it very expensive. Since 1985, many patents were issued, which employed complexes of Ru-salts instead of those of Rh-salts as hydrogenation catalysts in order to reduce cost. They were described in U.S. Pat. Nos. 4,631,315; 4,673,757; 4,747,707; 4,795,788; EP 0,405,266A2; 0,455,154A1; JP Sho-64-51405 etc. The advantage of Ru-salt complex catalyst is its high catalytic activity in hydrogenation, with the drawback of comparatively low selectivity due to side reactions and gel formation. Therefore, there is a need for a catalyst system which has higher activity and lower price and results in no gel in the hydrogenation reaction.
In addition, U.S. Pat. No. 5,135,901 discloses a catalyst system for oxosynthesis. It consists of three components, namely Rh compound, Ru compound and a cocatalyst (or ligand). The patent describes to introduce the above three components, without catalyst preparation in advance, into the reaction vessel. The raw materials are ethylene oxide, CO and H.sub.2 and the target product is either a .beta.-hyroxypropaldehyde or a .beta.-hydroxyl propionate.
It is an object of the present invention to provide a bimetallic complex catalyst system which is equal to conventional single Rh catalysts in activity and selectivity, but is much lower in cost.
It is another object of the present invention to provide a process for the preparation of the above mentioned bimetallic complex catalyst system.
It is a further object of the present invention to provide an improved hydrogenation process that can be carried out under mild conditions and free of gel formation.
It is still another object of the present invention to provide a hydrogenation process for unsaturated copolymers containing nitrile group besides carbon carbon double bond.
Other objects of the present invention can be apparent from the following detailed description.